Alzheimer's disease is the most common cause of dementia affecting nearly 18 million people worldwide and projected to double over the next 20 years. Without new and significant preventative or curative measures this growing problem will place a substantial burden on society in terms of both financial and emotional strains. Previous research has implicated over activation of thiol-proteases in AD progression. This is based primarily on the observation of an increased 'activation' state of various thiol-proteases in AD brain. However, other data suggest that thiol-proteases are not fully proteolytically active and that inhibition of thiol-proteases is more likely to contribute to AD pathology. Thus, there is an important discrepancy between the observed activation of thiol-proteases and their proteolytic activity in Alzheimer's disease. These contradictory findings regarding thiol-protease 'activation1 and thiol-protease 'activity' need to be resolved in order to move forward and determine the role of thiol-proteases in tau and Abeta accumulation as well as cell death/ dysfunction during Alzheimer's disease. To address this gap in our knowledge we will test the hypothesis that the 'activated' thiol-proteases are oxidatively inhibited at their active-site cysteines by specific oxidants in the hippocampus of Alzheimer's disease. Aim 1: Determine the activity of thiol-dependent proteases in Alzheimer's disease brain compared to age-matched controls within the vulnerable hippocampus and the non-vulnerable cerebellum. Based on our recently published work, we will show that thiol-protease activity, including calcium-dependent thiol-protease activity, is oxidatively inhibited in the hippocampus of AD brain compared to age-matched controls. Because AD degeneration is progressive, we will also determine the extent of thiol-protease oxidation over the progression of the disease using brain samples from various stages of Alzheimer's disease. Aim 2: Determine the oxidants responsible for thiol-protease oxidation in the hippocampus of AD brain. These studies will determine the extent of oxidation and the oxidants responsible for oxidation of active-site cysteines within individual thiol- dependent proteases in AD hippocampus. This hypothesis challenges an existing paradigm by suggesting thiol-protease activity in Alzheimer's disease is decreased (rather than increased) due to oxidation of the active site. The proposed research will have impact on future therapeutics involving anti-oxidant or protease inhibitor strategies in the treatment or prevention of Alzheimer's disease. [unreadable] [unreadable] [unreadable]